This project will focus on the role of cellular membranes in the secretory process of the pancreatic and parotid exocrine cells. Four main lines are to be pursued. 1) Conditions for the long term cultivation of populations of dispersed exocrine cells will be established in order to have available fully competent cells for the projected studies below. 2) Solid phase synthesis of caerulein, a peptidic secretogogue for the pancreas will be undertaken and derivatives of it suitable for topographic localization of hormone binding sites and for biochemical characterization of the binding protein by protein fractionation will be produced. These include ferritin tagged derivatives and radiolabeled and photoactivatable hormones which will be applied to isolated cells. 3) Topographic mapping of glycoproteins on the surface of isolated exocrine cells will be undertaken using ferritintagged plant lectins. These studies should detect regions of surface specialization anticipated from the structural and functional polarity of the cell. 4) Studies will be performed on isolated exocrine cells stimulated by secretogogues to test directly the hypothesis that secretory granule membranes are reutilized following exocytosis. Immunocytochemical procedures and radioautography of exogenously radiolabeled membrane constituents will be used to follow the fate of secretory granule membranes.